A new 20 percent tax break included in last year’s $1.5 trillion tax overhaul could wind up benefiting President Trump’s real estate empire given how the Treasury Department plans to implement the provision, several tax experts said.

On Wednesday, the Treasury Department issued a sprawling regulationoutlining the types of companies and professionals eligible to qualify as “pass-through” entities and get the 20 percent tax deduction. The widely anticipated rule has huge implications for law firms, real estate trusts, family farms and other companies that are structured so their profits are taxed as individual income for their owners.

The 184-page rule probably means a windfall for authors and small banks, who appear eligible for the 20 percent deduction, but a disappointment for dentists, who are not. It takes some steps meant to stop individuals and companies, such as law firms, from gaming the loophole to reduce their tax bills.

Tax experts say it appears to be largely a victory for business groups, who had argued for a more generous interpretation of a deduction that the congressional Joint Committee on Taxation estimates will primarily benefit Americans earning $1 million and up. “It looks like Treasury took some of the major concerns of the business community and the tax community seriously,” said Kyle Pomerleau, an economist at the Tax Foundation in Washington.

The regulation could also be a win for the president himself, because of how the regulation defines businesses that rely primarily on the “reputation or skill” of their owners to earn money. Those businesses are excluded from taking the deduction, but the regulation defines them narrowly, in a way that appears to allow the companies of the Trump Organization to qualify for the tax break at least in part.

Liberal groups said the guidance, as written, will help some wealthy Americans take advantage of the deduction. “This is a provision that we always thought would provide a windfall to high-income taxpayers,” said Jacob Leibenluft, the executive vice president for policy at the liberal Center for American Progress. “These rules not only fail to change that outcome, but may in fact exacerbate it.” ...

Owners of dental offices may not claim the deduction, it says, but owners of health spas may, because they do not directly provide medical services. Investment banks do not qualify, but banks that simply make loans and take deposits — like community banks — do. Paralegals may not, but the owner of a stenography service may. Football coaches do not qualify, but the owner of a company that cleans football stadiums would.

The regulation defines the “reputation or skill” exclusion narrowly. It does not appear to apply to writers, which means some authors with lots of book income could organize themselves as pass-through companies and qualify for the deduction. It does apply to celebrities who license their names or voices, endorse products or accept appearance fees, “including fees or income to reality performers performing as themselves on television, social media or other forums.”

That provision appears to allow a company that earns some of its income by licensing its owner’s name to apply the 20 percent deduction to other income that does not flow from licensing. That could be important for Mr. Trump, whose companies have licensed the Trump name to hotels and products around the world. Tax lawyers said Wednesday that the regulations could have prohibited Trump companies from deducting much more — if not all — of their income, instead of allowing the income streams to be separated.

“To the extent that he’s getting income from licensing the use of his name, it looks like he is ineligible for the deduction,” said Lily Batchelder, a New York University law professor and former Obama administration official. “But even if that licensing income was, hypothetically, 51 percent of his business’s income, I think it’s treated as a separate trade or business so he can get the deduction on the other 49 percent of his income.”

Ms. Batchelder said the narrow reading of the “reputation or skill” provision would allow tax breaks for wealthy owners of advertising agencies and other pass-through entities that trade largely on the abilities of their founders.

The regulation helps to resolve questions about whether some companies might need to restructure to comply with the law — or whether they would be allowed to restructure to game the rules. It outlaws a strategy known as “crack and pack,” where business owners split their operations into separate entities — for example, one that owns a doctor’s office and another that provides medical care — to avoid prohibitions on taking the deduction.